Normal murine endogenous lymphoid factor(s) inhibiting lymphocyte functions. I. In vivo effect on allogeneic tumor growth.

Murine lymphoid chalones and their in vivo effect was studied. Cytoplasmic extracts were prepared from normal murine spleen lymphocytes. When assayed in vitro, cytoplasmic extracts (CE) were able to inhibit a blastomitogenic phytohemagglutinin (PHA) response of syngeneic and allogeneic normal murine lymphocytes, as well as cell replication of murine lymphoma cells. CE also had an inhibitory effect on human lymphoblastoid cell line division but it had no effect on nonlymphoid cell division. In vivo, CE had an enhancing effect on a murine allogeneic tumor, probably by suppressing the host's immune rejection response.